Surface-Modified Pyrite with a Schwertmannite Shell: Enhancing the Application Performance of Pyrite-Mediated Advanced Oxidation Processes in a Continuous-Flow System

Most of the current pyrite-basedadvanced oxidation processes(AOPs)rely on a homogeneous catalytic mechanism mediated by leached Fe2+/Fe3+ from pyrite oxidation. While in continuous-flowwater treatment processes, the continual Fe2+/Fe3+ efflux limits pyrite dissolution and the corresponding hydroxylradical ((OH)-O-& BULL;) generation for contaminant degradation.To solve this bottleneck problem, a pyrite-schwertmannite (Sch)binary mineral named Sch@py(1:5) was prepared through a simple chemicalmethod where Sch serves as a surface shell coating on the pyrite core.Compared to the pyrite-H2O2 system, theSch@py(1:5)-H2O2 system exhibits significantlyslighter iron leaching and was verified to possess a heterogeneousFenton process dominant (OH)-O-& BULL; generation pathway,thereby eliminating the reliance of the Sch@py(1:5)-H2O2 system on Fe2+/Fe3+ concentrationsin water. Through shielding H2O2 from beingdirectly decomposed by pyrite and the associated Fenton sludge, theSch-pyrite core-shell structure improves the utilizationefficiency of H2O2 5.18 times and 1.15 timesthan that of the pyrite-H2O2 system inthe presence and absence of 0.21 g of Fe & BULL;L-1 Fenton sludge, respectively. Furthermore, the Sch shell endows pyritewith the coupling oxidation and adsorption capacity for organoarsenic-bearingcontaminants, thus enabling the Sch@py(1:5)-filled fixed bed to purify2451 BV of highly concentrated (0.1 mg of As & BULL;L-1) organoarsenic wastewater at a flow rate of 30 BV & BULL;h(-1). This study provides a novel strategy to improving the applicationpotential of pyrite, the commonly existing but underutilized mineralresource, in practical water treatment processes.